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Solutions Solutions (soln) are homogeneous mixtures of two or more pure substances. The solvent (solv) is present in greatest abundance. All other substances are solutes (solu). Volumetric flask {PrepASolu}

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Solutions Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute ( 50%). Homogeneous Heterogeneous

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Solutions Student, Beware!: solution vs. reaction Just because a substance disappears when it comes in contact with a solvent, it doesn’t mean the substance dissolved. Dissolution is a physical change—you can get back the original solute by evaporating the solvent. If you can’t, the substance didn’t dissolve, it reacted. Mg (s) + 2 HCl (aq)  H 2 (g) + MgCl 2 (aq) Cu(NO 3 ) 2 (s) Cu(NO 3 ) 2 (aq) H2OH2O H2OH2O

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Solutions How Does a Solution of Salts in Water Form? NaCl (s) Na + (aq) + Cl - (aq) dissociation + H 2 0 The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles. Example: {NaCl + H 2 O*}

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Solutions Supersaturated  Solvent holds more solute than is normally possible at that temperature.  These solutions are unstable; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask. {*SuperSat1}SuperSat1 {*SuperSat2} Concentration of Solutions (General)

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Solutions Factors Affecting Solubility of Gases in Solution: (2) Pressure {Henrys Law} The solubility of liquids and solids does not change appreciably with pressure. The solubility of a gas (S g ) in a liquid is directly proportional to its pressure (P g ). S g P g

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Solutions The opposite is true of gases:  Gases in carbonated soft drinks are less soluble when warmed.  Warm lakes have less O 2 dissolved in them than cool lakes. Factors Affecting Solubility of Gases in Solution: (3) Temperature

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Solutions ppm = mass of solu A in solution total mass of solution  10 6 Parts per Million (ppm) ppb = mass of solu A in solution total mass of solution  10 9 Mass % of A = mass of solu A in solution total mass of solution  100 or 10 2 Mass Percentage (%) (parts per Hundred) 50. g of NaCl in 100.mL of H 2 O g of NaCl in 100.mL of H 2 O 0.000,000,5 g of NaCl in 100.mL of H 2 O Parts per Billion (ppb) hundred million billion

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Solutions moles of substance A total moles in solution (A+B+∙∙∙) X A = Mole Fraction (X) You can calculate the mole fraction of either the solvent or of the solute — make sure you find the one you need for your calculations! What are the mole fractions of methanol and water in a solution containing 128g CH 3 OH (MW=32.0) and 202 mL of H 2 O (MW=18.0)? Which is the solute and the solvent? Mole fraction of Solvent: Mole fraction of Solute:

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Solutions moles of solute kg of solvent m = Molality (m) Because both moles and mass do not change with temperature, molality (unlike molarity) is not temperature dependent. What is the molality of a solution containing 128g CH 3 OH (MW=32.0,  C) and 202 mL of H 2 O (MW=18.0,  C)?

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Solutions Problem: What is the molality (m) of a 2.0M NaCl solution at 25 0 C if its density is 1.2 g/mL? Changing Molarity to Molality If we know the density of the solution, we can calculate the molality from the molarity, and vice versa. mol of solute L of solution M = mol of solute kg of solvent m = = 1.8 m NaCl

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Solutions 1. Vapor Pressure ( P vap ) Lowering Because of solute-solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase. Therefore, the vapor pressure of a solution (P A ) is lower than that of the pure solvent (P  A ). {PureSolv} {*Solution} P A = X A  P  A

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Solutions Raoult’s Law: P A = X A P  A where X A is the mole fraction of solvent A P  A is the normal vapor pressure of the pure solvent A at that temperature P A is the new vapor pressure of solution at that temperature Consider: X A = 1 X A = 0.9 X A = 0.5 {VapPress.WaterVsEthGlycol}

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Solutions Freezing Point Depression The change in freezing point is proportional to the molality of the solution :  T f = K f  m Here K f is the molal freezing point depression constant of the solvent.  T f is subtracted from the normal freezing point of the solvent. {f.pt. Equil} {f.pt. Lower}

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Solutions Boiling Point Elevation The change in boiling point is proportional to the molality of the solution:  T b = K b  m where K b is the molal boiling point elevation constant, a property of the solvent.  T b is added to the normal boiling point of the solvent.

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Solutions Freezing Point Depression & Boiling Point Elevation Note that in both equations,  T does not depend on what the solute is, but only on how many particles are dissolved.  T f = K f  m  T b = K b  m

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Solutions Osmosis The movement of water from an area of high concentration to lower concentration (diffusion) across a semipermeable membrane (SPM), until a homogeneous solution has been formed (equilibrium). The SPM allows smaller particles (water) to pass through, but blocks other larger particles. Diffusion of water across a SPM. Diffusion The movement of particles from an area of high concentration to lower concentration until a homogeneous solution has been formed.

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Solutions Osmosis In osmosis, there is net movement of solvent from the area of higher solvent concentration (lower solute concentration) to the area of lower solvent concentration (higher solute concentration). {*OsmoPress} Solvent Solution

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Solutions Osmosis in Cells If the water concentration outside the cell is more than that inside the cell, the solution is hypotonic (low in solute). Water will flow into the cell, and hemolysis results. {EggOsmoPres} H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O High Water Low Water H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O (high solute) (low solute)

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Solutions Osmosis in Blood Cells If the water concentration outside the cell is lower than that inside the cell, the solution is hypertonic (high in solute). Water will flow out of the cell, and crenation results. Isotonic: equal concentrations. H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O (salt water) (salt water) High Water (high solute) (low solute) H2OH2O H2OH2O H2OH2O H2OH2O

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Solutions Reverse Osmosis The method of purifying liquid by pushing it through a semi-permeable membrane. Pressure is utilized to reverse the natural osmotic flow through a synthetic membrane so that pure water molecules pass through and impurities are flushed away. What exactly is Reverse Osmosis? Reverse Osmosis is the method of purifying liquid by pushing it through a semi- permeable membrane.Osmosis is the process by which water and nutrients are supplied to living cells. The natural flow of water is from a dilute to a concentrated solution across a cell wall. Cell walls are natural, selective semi- permeable membranes, which allow certain materials to pass through but reject others.In a reverse osmosis system, pressure is utilised to reverse the natural flow through a synthetic membrane so that pure water molecules pass through and impurities are flushed away. {RevOsmo} Membrane H2OH2OH2OH2OH2OH2O Contaminated water Reverse Osmosis What exactly is Reverse Osmosis? Reverse Osmosis is the method of purifying liquid by pushing it through a semi- permeable membrane.Osmosis is the process by which water and nutrients are supplied to living cells. The natural flow of water is from a dilute to a concentrated solution across a cell wall. Cell walls are natural, selective semi- permeable membranes, which allow certain materials to pass through but reject others.In a reverse osmosis system, pressure is utilised to reverse the natural flow through a synthetic membrane so that pure water molecules pass through and impurities are flushed away. {RevOsmo} Membrane H2OH2OH2OH2OH2OH2O Pure H2OH2O Contaminated water

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Solutions Determining Molar Mass from Colligative Properties We can use the effects of a colligative property such as freezing point depression to determine the molar mass (MM) of a compound. A solution of an unknown nonvolatile electrolyte was prepared by dissolving 0.250g of the substance in 40.0 g of CCl 4. The b. pt. of the resultant solution was C higher than that of the pure solvent. What is MM of solute? The K b for CCl 4 is C/m.  T b = K b  m

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Solutions Determining Molar Mass from Colligative Properties We can use the effects of a colligative property such as osmotic pressure to determine the molar mass of a compound.  = MRT The osmotic pressure of a protein solution was 25 0 C to be 1.54 torr. The solution contained 3.50 mg of protein dissolved in water to make 5.00 mL of solution. Determine the molar mass (MM) of the protein.

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Solutions van’t Hoff Factor One mole of NaCl in water does not really give rise to two moles of ions. Some Na + and Cl − reassociate for a short time, so the true concentration of particles is somewhat less than two times the concentration of NaCl. Reassociation is more likely at higher concentration. Therefore, the number of particles present is concentration dependent.

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Solutions Colloids in Biological Systems These molecules can aid in the emulsification of fats and oils in aqueous solutions. {Cotton Fabric Softener} {Micelle}

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Solutions Suspension: heterogenousheterogenous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre.[1] The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents.solidsedimentation[1]agitation